Apple's sales of its popular iPhone, iPad and Mac computers are going up, but the company's tech support quality is going down, according to a recent study.

Minnesota-based research firm Vocal Laboratories shows Apple's lead in tech support quality is slipping while customer satisfaction scores for HP are improving.

Apple continues to lead Dell and HP in customer service quality for phone-based technical support but customers are reporting more problems with the automated part of the call, the latest study from Vocalabs shows.

In telephone interviews immediately following a support calls, Vocalabs found that 58 percent of customers were "very satisfied" with the experience in the first six months of 2011, compared to 47 percent of Dell customers and 53 percent of HP customers.

But Apple's satisfaction score is down 15 points from the same period the year before, while HP improved nine points over the past two years.

"Apple used to be well ahead of the pack in tech support," said Peter Leppik, CEO of Vocalabs. "Now it would be fair to say that they are merely at the front of the pack. Apple used to lead on nearly every metric for support quality. Now there are several metrics where Apple is tied with its competition, or even trails."

Customers remain highly satisfied with Apple's support agents, with 77 percent of customers being "very satisfied" with the technician in the first six months of the year, the survey found, compared to 56 percent of Dell customers and 61 percent of HP customers.

But in the automated portion of the customer service survey, only 24 percent of Apple's customers reported being "very satisfied" trailing Dell's 36 percent and HP's 40 percent.

In that portion of Vocalabs' survey, 40 percent of Apple customers reported a problem with the automated part of the call, nearly double the 21 percent rate from a year ago.

The National Customer Service Survey from Vocalabs tracks customer service quality in several industries, using telephone interviews conducted with a customer immediately after a customer service experience. The survey is underwritten and conducted by Vocalabs, independently of any companies covered.